The present invention relates to a multifocal intraocular lens for implantation in the human eye having a plurality of concentrically-arranged regions alternately powered for differing vision ranges, e.g., near and far vision, surrounding a substantially circular central region.
Various lenses have been disclosed which have a circular central region surrounded by a single ring. For example, U.S. Pat. No. 3,420,006 discloses bifocal contact lenses in which a central region powered for distance vision is surrounded by a ring powered for near vision, while U.S. Pat. No. 3,270,007 discloses the reverse configuration. U.S. Pat. Nos. 3,726,587 and 4,636,049 also disclose bifocal contact lenses in which a central region powered for near vision is surrounded by a ring powered for far vision. These latter lenses are said to work better than earlier lenses having the near-vision portion outside the distance portion.
U.S. Pat. No. 4,573,775 discloses soft multifocal contact lenses having a vertical array decreasing power. U.S. Pat. No. 4,580,882 discloses a contact lens in which the power varies continuously outward from a central area for distance vision.
U.S. Pat. No. 4,636,211 discloses bifocal intraocular lenses having a central region powered for near vision and a single surrounding ring powered for distance vision.
Each of these earlier disclosures offers some optical theory as to the reason for operation of a particular lens design, and U.S. Pat. Nos. 3,726,387, 4,636,049 and 4,636,211 specify particular preferred sizes for the near and far vision portions. Such size specifications represent a compromise, however, in order to provide adequate light collecting area in both the far and near vision segments if significant pupillary excursion occurs under different lighting conditions. This compromise is necessary if the known lenses are to provide both distance and near vision at both extremes of high and low lighting levels and thus small and large pupillary aperature, but leads to decreased efficiency of near vision at low lighting levels (assuming a near-vision central portion) and decreased efficiency for far vision at high light levels. The claimed invention overcomes this difficulty, thus providing bifocal intraocular lenses which more closely approximate the vision range of a natural lens.